Structural materials containing cork granules are well known, with the majority of said materials being rigid cork composition materials for bulletin boards, wall tile, or the like. However, it has been known to make a flexible cork composition by filling a polyvinyl chloride resin material with cork granules, so that the resin holds the granules together in a flexible structure.
However, the cork granules remain or become dry and brittle, so that the resulting product is only slightly flexible without resulting in breakage of the cork granules, even though the vinyl binder material itself is flexible.
Other compositions made of cork granules constitute a mixture of gelatin glue and glycerine as a plasticizer for the cork, to soften it, plus water. This composition, after formation, tends to dry out due to slow loss of the glycerine from the cork, resulting in shrinkage of the composition.
By this invention, a formulation is provided in which the plasticizer in the cork is retained within the cork granules, and does not migrate into the binder or matrix of the composition, with the result that the loss of glycerine or other polyol-type plasticizer proceeds at a much slower rate than has been known in the prior art. Accordingly, thin sheets of the composition of this invention may be flexible, and may retain their flexibility for a long period of time due to inhibition of the loss of the glycerine or other polyol plasticizer from the cork granules by the use of the principles in accordance with this invention.